This invention relates to a pilot operated valve with pressure relief and to a method of relieving pressure on a pilot operated valve. Such pilot operated valves, and more particularly such pilot operated diaphragm valves may be utilized in a refrigeration system for liquid, suction, or hot gas refrigerant service, or in a steam distribution system or the like.
Typically, in many refrigerant circuits, remotely operable valves are provided for switching the refrigerant circuit from one mode of operation (e.g., a cooling mode) to another mode of service (e.g., a heating or defrosting mode). For example, in a supermarket refrigerated display case, the refrigerant system may undergo a heating and defrosting cycle periodically thereby to maintain the evaporator and other surfaces of the refrigeration system free of frost and ice. However, during the majority of the time, the refrigerant system will operate in a normal cooling mode and the heating and the defrosting cycle will last only a relatively short period of time. Typically, these remotely operable valves may be either normally open or normally closed, depending upon their location within the refrigerant circuits.
Heretofore, prior art solenoid operated refrigerant valves, such as illustrated in FIG. 6, were in common usage. As was typical, these prior art solenoid operated refrigerant valves had a pilot valve member movable between an open and a closed position by means of a solenoid actuator for selectively opening a pilot passage. When the pilot passage was closed, fluid pressure from the inlet or high pressure side of the pilot actuated valve would bleed through an orifice in the diaphragm valve and act against the back face of the diaphragm valve in such manner that the pressure force together with a spring force would move the diaphragm valve from its open to its closed position in engagement with the valve seat of the main flow path through the valve thereby blocking the flow of refrigerant. With the flow of refrigerant blocked, the pressure in the flow passage of the valve would be significantly less than the inlet pressure upstream from the valve seat and thus the fluid pressure on the backface of the diaphragm valve together with the spring force would positively hold the valve in its closed position. Upon energizing the solenoid actuator, the pilot valve member would be moved clear of the pilot valve seat thereby permitting the fluid pressure acting against the back face of the diaphragm valve to be relieved therefrom at a rate greater than fluid pressure could flow from the upstream side of the flow passage to the back face of the diaphragm valve thus permitting the fluid pressure on the downstream side of the diaphragm valve to force the diaphragm valve open against the bias of the spring acting to close the diaphragm valve.
In certain applications, it is desirable to limit the pressure difference across the solenoid valve to a predetermined upper limit. In order to limit the pressure across the solenoid valve to a predetermined limit, it was typical to provide a pressure relief valve in parallel with the solenoid operated valve, as illustrated in FIG. 5. This pressure relief valve would, of course, be actuated upon the pressure difference between the inlet and outlet side of a prior art solenoid operated valve exceeding a predetermined limit thereby permitting refrigerant to flow around the closed pilot operated solenoid valve. However, the requirement of providing this relief valve, together with the necessary tubing and fittings so as to incorporate the relief valve in the refrigerant circuit is complicated and therefore expensive.
Reference may be made to such U.S. patents as: U.S. Pat. Nos. 1,505,032, 2,705,608, 2,940,722, 3,114,532, 3,115,366, 3,208,716, 3,362,679, 3,363,433, 3,806,081, 3,943,795, and 4,270,276 for prior art valves in the same general field as the valve of the instant invention.